Rachel's weakness is Dark magic, therefore, Sonic can erect a barrier around Rachel to protect her from the Dark magic in the atmosphere around them. (this cant, however, protect her from Dark energy directed at her by an attack)
Reason #2:
The only thing that Sonic can't do, is swim, henceforth, Rachel, being part mermaid, can work with sonic when forced into an aquatic environment.
(once again, please, no hate comments, this is an "opinion article", so i would appreciate it if Ты would keep yur hate Комментарии (if any hate comments, tho i cant see how Ты could have any hate Комментарии with something like this) to your own thoughts. thank Ты very much!)